Single-walled carbon nanotubes are a kind of nano-material with great potential for research. Based on its nanoscale size and special structure, single-walled carbon nanotubes have good electrical properties, photoelectric properties and semiconductor-type properties. Single-walled carbon nanotubes can be divided into two types: metallic type and semiconducting type. Because of the different application of these two types of single-walled carbon nanotubes, they need to be distinguished. With the application of carbon nanotubes more and more widely, how to distinguish metallic carbon nanotubes and semiconducting carbon nanotubes become a hot research.
Conventional methods for distinguishing metallic carbon nanotubes and semiconducting carbon nanotubes include Raman spectroscopy or electrical measurement methods. The complexity of the operation of these methods lead to lower efficiency. Scanning electron microscopy, because of its high discrimination efficiency, more and more people use it to characterize carbon nanotubes. Referring to FIGS. 1 and 2, in the conventional method of characterizing carbon nanotubes using a scanning electron microscope, a lower (1 kV or so) accelerating voltage is used in order to obtain a clear and high contrast photograph. In the carbon nanotube photo obtained by the traditional scanning electron microscope characterization method, the electrical conductivity of carbon nanotubes is related to the color of the carbon nanotubes in the photo. The lighter the color, the better the electrical conductivity. However, the color of all the carbon nanotubes including the metallic carbon nanotubes and the semiconducting carbon nanotubes is lighter than the color of the photo background. When the metallic carbon nanotubes and the semiconducting carbon nanotubes are both present in the photo, it is very hard to distinguish the carbon nanotubes having middle color, such as gray carbon nanotubes. Therefore, the accuracy of the traditional scanning electron microscopy method for characterizing carbon nanotubes in the identification of carbon nanotubes species is not high enough. Moreover, since the color of both the metallic carbon nanotubes and the semiconducting carbon nanotubes displayed in the photo is lighter than the photo background color, when there is only one type of carbon nanotubes in the photo, it is difficult to judge that the carbon nanotubes in the photo are metallic carbon nanotubes or semiconducting carbon nanotubes.
What is needed, therefore, is to provide a method for characterizing carbon nanotubes that can overcome the above disadvantages.